A subscriber identity module (SIM) configured in a mobile device or a smart device in the form of a chip card contains essential individual subscriber data that is required for facilitating mobile services. A typical SIM card comprises an integrated circuit chip that is intended to securely store the international mobile subscriber identity (IMSI) number and the related key/s, which may be used to identify and authenticate subscribers/users on the mobile devices along with other information including, but not limiting to, its unique serial number (ICCID), international mobile subscriber identity (IMSI) number and security authentication and ciphering information. SIM cards are typically designed to be transferable between different mobile devices. Further, the SIM circuit forms a part of the function of a Universal Integrated Circuit Card (UICC) physical smart card (referred to as ‘SIM’ card herein). Also, the SIM comprises a SIM file system that further consists of the Master File (MF), Dedicated Files (DFs) and the Elementary Files (EFs) that are mainly used for controlling the user equipment's (UE) behaviour in the network by facilitating a secured registration to desired network, deciding which services should be restricted and allowed and subsequently maintaining a status list of the EF and DF files.
Further, each subscriber is identified by a unique International Mobile Subscriber Identity (IMSI) which consists of the PLMN (MCC, MNC) of a network operator and the Mobile Subscription Identification Number (MSIN). There are different network operators (either available in same country or different country) which provide such voice and data services to subscribers not only of their own subscribers but also from other networks. Therefore, in an exemplary instance, of international roaming, when the subscriber (Roaming Subscriber (RS)) leaves the home network and moves to a foreign location (Roamed Network (RN)), the user equipment receives services from another network within the same country due to unavailability of the home network as per bilateral roaming agreements between the home and the roamed network operators.
In recent years, wireless communication networks have undergone tremendous growth and commercialization, thereby resulting in increased number of services and features offered on such devices. Therefore, it has now become essential to provide good quality roaming network for maintaining a network operator's brand value for roaming services, since these network operators provide a plurality of subscribed services to the users/subscribers by facilitating registration, authentication, location updating, handovers, call routing, etc. Currently, the wireless networks are being configured to provide an Auto IMSI Switch SIM application in case of international roaming by facilitating swapping the IMSI (home IMSI) of the home network operator with an IMSI (Global IMSI) of a global Network Operator. With the updated IMSI, the user equipment may easily avail services in international roaming. However, there are two prerequisites for successful functioning of the Auto IMSI Switch, one of which is that the Auto IMSI Switch SIM application is able to detect rejection of user equipment's in attempting to attach to the available network followed by the second prerequisite that the SIM application is able to affirm that the user equipment is in the international location.
Additionally, for efficient swapping of the IMSI, the user equipment should be able to communicate with the subscriber identity module using a variety of commands such as proactive commands (as specified in the 3GPP TS 31.111 standard, including, but not limiting to, PROVIDE LOCAL INFORMATION (PLI) and REFRESH). The PLI proactive command is typically used to request the user equipment to transmit the current local information directly to the subscriber identity module, wherein the current local information includes but not limited to, local information relating to user equipment, IMEI, network measurement results, current date and time zones, language settings, current access technology, current network search mode and battery status. Further, in situations where the attach request of the user equipment cannot be accepted by the international roaming network, the international roaming network rejects the attach request based on appropriate cause code value specified in the 3GPP TS 24.301, including, but not limiting to, Illegal user equipment, unavailability of cells in tracking area, non-allowable EPS service, non-allowable tracking area and non-allowable PLMN. The existing technologies for Auto IMSI Switch SIM application provide a solution by using a particular Elementary File (EF) of the SIM card viz. EFFPLMN. When the user equipment having the home IMSI sends the attach request to the international roaming network and receives an attach reject with reject Cause such as “PLMN Not Allowed”, the user equipment updates the Forbidden PLMN list in the USIM FPLMN elementary file (EFFPLMN) with the PLMN value of the roamed network from which it received the reject message resulting in triggering of the Auto IMSI Switch SIM application to replace the home IMSI by global IMSI. Thereupon, when the user equipment having the global IMSI re-sends the attach request, the international roaming network will be attached successfully with the user equipment. Similarly, the Auto IMSI Switch SIM application can be triggered when the user returns back to the home network from the international roaming. However, these existing solutions for Auto IMSI Switch SIM application poses certain limitations, one of which is inability to update the EFFPLMN values when the reject cause is not “PLMN Not Allowed” i.e. in the event the reject cause is not “PLMN Not Allowed”, the Auto IMSI Switch SIM application cannot be triggered. Thus, this Auto IMSI Switch SIM application is not a robust criteria.
Another limitation relates to a limited amount of memory and processing power available on the SIM card. In an exemplary event, the size of EFFPLMN may vary from subscriber identity module to subscriber identity module based on the operator requirements and therefore, different user equipments update the EFFPLMN differently based on their implementation since there is no standard definition to update the FPLMN list. Therefore, this approach is less efficient and poses certain limitations, inter alia, the Auto IMSI Switch SIM application compares the updated values with the previous values to detect the updation.
Accordingly, in order to overcome the aforementioned problems inherent in the existing solutions for Auto IMSI Switch SIM application, there exists a need of an efficient mechanism to create holistic criteria for Auto IMSI Switch SIM application by using the PLI proactive commands independent of the cause code sent by any user and can work regardless of the cause code received.